Sorry for being a pain in the*%$@! but, I’m confused when Landreo stated “the 10 SI diode trio is for the field current and likely would not survive in a battery charger due to the higher current”. This particular generator weakness was the diode trio and back in the day I replace a lot of them. I know how to test and diagnose this generator and probably when I was trained on it I was taught the operation of the diode trio function and rectifier, but have since forgotten. When you stated; diode trio is for the field current it seems as though the diode trio only operates low amperage part of the generator. This part confuses me because it’s attached to the rectifier and what I can see in the diagram is; the voltage regulator grounds the diode trio when current is required.

This is how the generator operates

With the generator operating, AC voltages are generated in the stator windings, and the stator supplies DC field current through the diode trio, the field, TR1, and then through the grounded diodes in the rectifier bridge back to the stator. Also, the six diodes in the bridge rectifier change the stator AC voltages to a DC voltage which appears between ground and the generator "BAT" terminal which is connected to the storage cell. (Battery)

When I originally made the suggestion, I was thinking about the diodes from the early alternators, without the built in regulator. They predate the 100+ amp alternators and may not be able to handle the 70 amp boost rate either.

Hoping my memory is correct, Chevrolets started using alternators in the 1963 model year. External regulator. Delco 10DN. The largest of those I ever saw was rated 63 amps and many were 37 amps. I do not know if all of them used the same diodes. Chevy started using the internal regulator in 1974. Delco 10SI. Some of those were just 37 amps also.

Added: The reason I mentioned Chevrolet, some of the higher end GM products (Cadillac, Buick) used alternators earlier. Some of those were oddball items that were produced for only a short time and evidently were made obsolete by rapid advances in design and construction of alternators. By the time Chevy got them, the design was well established and volume production was in progress.

I have a Delco 15SI as a conversion on a Farmall 140. Electrical hookup identical to the 10SI. It is from a Buick, 70 amp, $18.00 at the wrecking yard. Overkill on the amperage! Slightly larger than a 10SI, but plenty of room for it on that tractor. Shop-made mount to hold it in close to the engine on that tractor was a challenge, for me at least. Alternators tucked in close are much less subject to damage.I am getting too far off subject.

That is about what I remember on the externally regulated Delco alternators as well. I think they were common until about 1970. The change to internal regulation was probably not done all at once. Delco evidently had several different diodes with different current capabilities. They no doubt shared a size/shape. Some of the aftermarket suppliers had a single replacement that was cross listed to several Delco numbers (example SMP's D1P and D1N). They were probably sized for the highest capacity they crossed to. Check this page (and the following):http://www.gmpartswiki.com/getpage?pageid=18675It appears the one I pointed at was used up to 52 amps and only in '62. I know that the Corvair alternator (used diodes 1959829 and 1959830) came standard at 37 amps and was changed to 47 amps by only changing the rotor. The same diodes are listed as high as 61 amps. By the way, if you start chasing any of these numbers, the page I pointed at above has an important typo. The group number should be 2.319, not 3.219.

When you stated; diode trio is for the field current it seems as though the diode trio only operates low amperage part of the generator. This part confuses me because it’s attached to the rectifier and what I can see in the diagram is; the voltage regulator grounds the diode trio when current is required.

The diode trio is only for the field current through the regulator, standard "A" circuit like cub voltage regulators. THe diode trio is not connected to the bridge output. They share a common connection with the stator windings but the diode trio gets AC current from the stator not the DC coming out the other side of the bridge. The AC connection is all they have in common.

With the generator operating, AC voltages are generated in the stator windings, and the stator supplies DC field current through the diode trio, the field, TR1, and then through the grounded diodes in the rectifier bridge back to the stator. Also, the six diodes in the bridge rectifier change the stator AC voltages to a DC voltage which appears between ground and the generator "BAT" terminal which is connected to the storage cell. (Battery)

The field current starts at the stator windings to the common connection with the stator, diode trio, bridge. The bridge goes to the battery as high amp dc, AC from the stator goes to the trio to form the dc field current. No connection between the bridge and the trio outputs. The trio dc goes to the voltage regulator then to the field windings and then the ground. D2, zener diode, with a resistor voltage divider is the voltage sensor, t2 is the voltage on off that controls t3 then the power transistor t1 which controls the field current. D1 is a commutator diode for voltage spikes and does not affect directly the operation of the regulator nor does it carry any field current. The one 10 si regulator I unpotted and reversed actually had only t1 and t2. THe posted diagram may apply to a 12si

The end result is that the field and diode trio are independent of the bridge rectifier. The field current likely is only a few amps so no need for a large diode capacity for the diode trio.

I got my old book back out from which I copied the diagram and the caption stated 10SI-12SI. This is a GM training book and not a Delco book so it could be wrong. I know all the 10SI’s were replaced under warranty with the 12SI’s.

Trivia The model 10SI Delco built alternator is the first generation, SI series alternator. It was introduced on the 1969 Corvette, and by 1973 most GM built cars and light trucks used this model alternator. It was an option with at least some 70, 71, and 72 GM cars, although it rarely showed up in those years, except for on the Corvette where it was standard equipment.

Assembled with all original GM components, the model 10SI alternator had a maximum output rating of 63amps. Output rating is determined by the windings in the alternator, and not all model 10SI alternators had the same windings.

There were 10SI alternators with 37amp, 42amp, 55amp, 61amp, and 63amp ratings. The smaller amp output rated alternators were installed on cars with no air conditioning, and few electrical accessories. The 61amp output rated 10SI was very commonly installed on 8cylinder cars, with factory air conditioning option.

For luxury cars loaded with electrical accessories, there were larger and more powerful models of alternators than the 10SI. A few of the full size Buick, Pontiac, Cadillac, or Oldsmobile could be had with model 12SI - 15SI, or possibly the model 27SI alternator. The 15SI and 27SI alternators looked the same, but were scaled up in size. They were physically larger and heavier, and output ratings were often 70amp, 80amp, and 100amp.

I’m really good at doing nothing…With that said…I’m really, really good at doing nothing

JachF,I reread your post and believe I misunderstood your comments. I took the grounding diode to be in reference to D2 in the voltage regulator which is why I was discussing the regulator components, but now it is clear you were talking about the bottom 3 diodes in the bridge. The field current does get to the ground through those 3 diodes.

Sorry, I can’t write and chew gum at the same time. I was talking about the diode trio from the rergulator to the bridge. As you explained it does ground the voltage regulator on one side and the diode trio is not connected to the bridge output. They share a common connection with the stator windings but the diode trio gets AC current from the stator (low amps) not the DC coming out the other side (output to battery) of the bridge.

The direct current from the rectifier bridge output terminal outside the generator supplies the battery via battery cable with potential high amperage.

Thank you again for your input and knowledge it was an honor and I learned a lot!

I’m really good at doing nothing…With that said…I’m really, really good at doing nothing

Mr. Schulz composed a very well laid out section devoted to generation and conversion to DC along with outstanding troubleshooting procedures which included a slew of GM technical photos and data in Unit 44, "Charging System (Generators)". The following unit, "Regulation" is also very good to reference back to for regulation problem solving.

I also have/had a very good Leece Neville 130 ampere hour technical manual which I seem to be having trouble locating at the moment.

If any of you gentlemen would ever find the need to consult my Schulz manual, I will kindly lend it to you for your reference. Just ask and I will drop it in the mail.

I had collected 2 battery chargers, one intermittently failing, the other completely NFG. Upon inspection I eventually found both of them to contain opens in the secondary circuitry, most likely at my hand from demanding too much from them. I spent way too much time isolating and testing each component with no factory data base to compare my results, but it was challenging and fun to get them fully functional again.

I think Beaconlight hit the nail on the head. Cracked wire. I parted out Dad's old charger, only to find it was the cables. Had a radio shop check the electronics, they said "dead". Saved the cables, and went to use them, no go:(

The two bridge rectifiers I ordered arrived. Supposedly rated 1000 volts, 50 amps. They look small for 50 amps and no way are the terminals suitable for 50 amps sustained current. Two different testers were used to verify the condition of one of the rectifiers--and that has created confusion for me. My BK Precision meter shows 1 when set for Ohms and the leads are not touching. It has no symbol for Infinity, which is what it really should read. Tested two adjacent terminals, one reading was the 1, for Infinity or open circuit, no continuity. Reversed the leads on the terminals and the readings are from 639 to 645-- all pretty close to each other and indicating conductance-- but not much. I have not applied AC power to the bridge, only the DC of the meter. A DC resistance of 640 Ohms suggests that at 6 volts, the current would be 0.009 amps, at 120 volts the current would be 0.178 amperes. I thought I understood these concepts well but something is just not right.So what am I missing or not understanding?

The second part is that here in my desk, there is a Harbor Freight multimeter- the cheapest they sell-- and occasionally offer as a freebee. Occasionally useful in a hurry. It too shows the 1 when the leads are separated in the Ohms function. Same on the bridge in one position. But when I reverse them on the bridge, the display flashes some numbers for a split second, then goes back to the 1. Never displays a readable resistance value. How to explain that?